The steam reviews are mixed, compared to overwhelmingly positive for L4D2. It's also Windows exclusive with Easy Anti-Cheat so it can't run on Linux. (It's a coop game, who cares about cheating there??)
B4B does have a human vs zombie multiplayer mode
However, that mode is nothing like the versus mode people actually wanted.
Cheats can also be used to grief other players in the match making queue.
I haven't played it, but this video gives the impression that it is much less polished in comparison to its predecessors. However it could just be nitpicking.
https://www.youtube.com/watch?v=EdRLNUGmFC8
I would recommend giving this video a watch. It'll show you just how much care and attention to detail was put into L4D 1 and 2: https://www.youtube.com/watch?v=EdRLNUGmFC8
It's okay. The difficulty ramp-up is really steep to the point where once you finish the easier difficulties it just gets way too hard. Maybe if you play with friends it would be different, but I was mostly solo queueing.
That being said... it was a lot of fun until I got frustrated with it! It's on the PC game pass.